Key Concepts in Geomorphology

PART I
Geomorphology and Its Tools 3
Earth’s Dynamic Surface 5
Introduction 5
Geosphere 6
Isostasy 6
Tectonics 11
Lithology and Structure 13
Hydrosphere 14
Climate and Climate Zones 14
Hydrologic Cycle 16
Biosphere 16
Geographical Distribution of Ecosystems 18
Humans 20
Landscapes 20
Process and Form 22
Spatial Scales 22
Temporal Scales 23
Unifying Concepts 24
Conservation of Mass 24
Conservation of Energy 24
Material Routing 24
Force Balances and Thresholds 25
Equilibrium and Steady State 27
Recurrence Intervals and Magnitude-Frequency Relationships 28
Applications 28
Selected References and Further Reading 30
Digging Deeper: Why Is Earth Habitable? 31
Worked Problem 34
Knowledge Assessment 34
A Brief History of Geomorphology 36
Geomorphologist’s Tool Kit 43
Introduction 43
Characterizing Earth’s Surface 44
Field Surveys 44
Active Remote Sensing 46
Passive Remote Sensing 47
Digital Topographic and Landscape Analysis 47
Relative Dating Methods 48
Landform Degradation 48
Rock Weathering and Soil Development 50
Rock Varnish 50
Calibrated Relative Dates 50
Numerical Dating Methods 52
Dendrochronology 52
Radiocarbon Dating 53
K/Ar Dating 54
U/Th Dating 56
Luminescence Dating 56
In-Situ Cosmogenic Nuclide Analysis 58
Measuring Rates of Geomorphic Processes 59
Sediment Generation Versus Sediment Yield 59
Landscape Change at Outcrop and Hillslope Scales 61
Landscape Change at Basin Scales 63
Erosion Rates over 10^6 to 10^8 Year Timescales 63
Experiments 63
Field Experiments 63
Laboratory Experiments 65
Numerical Models 66
Proxy Records 66
Applications 67
Selected References and Further Reading 68
Digging Deeper: How Does a Dating Method Develop? 69
Worked Problem 72
Knowledge Assessment 72
PART II
Source to Sink 75
Weathering and Soils 77
Introduction 77
Physical Weathering 80
Exfoliation 80
Freeze–Thaw 82
Thermal Expansion 82
Wetting and Drying 83
Chemical Weathering 83
Mineral Stability 84
Oxidation and Reduction 85
Solution 85
Hydrolysis 86
Clay Formation 87
Hydration 88
Chelation 89
Cation Exchange 89
Soils 89
Soil-Development Processes 89
Factors Affecting Soil Development 90
Processes and Rates of Soil Production 91
Soil Profiles 91
Soil Classification 95
Soils and Landscapes 99
Soil Development over Time 99
Soil Catenas 99
Paleosols 100
Weathering-Dominated Landforms 101
Inselbergs and Tors 102
Duricrusts 103
Applications 104
Selected References and Further Reading 105
Digging Deeper: How Fast Do Soils Form? 106
Worked Problem 109
Knowledge Assessment 110
Geomorphic Hydrology 111
Introduction 111
Precipitation 112
Duration and Intensity 113
Recurrence Intervals 113
Precipitation Delivery 114
Climate Effects on Hydrology and Geomorphology 115
Evapotranspiration 116
Evapotranspiration Rates 116
Actual Versus Potential Evapotranspiration 116
Geomorphic Importance of Evapotranspiration 116
Groundwater Hydrology 118
Infiltration: Moving Water into the Ground 119
Moving Water Through Earth Materials 120
Hydrologic Flowpaths 122
Surface Water Hydrology 126
Hydrographs 126
Interactions Between Groundwater and Surface Flow 129
Flood Frequency 130
Water Budgets 132
Hydrologic Landforms 133
Applications 137
Selected References and Further Reading 137
Digging Deeper: Humans, Hydrology, and Landscape Change—What’s the Connection? 138
Worked Problem 141
Knowledge Assessment 142
Hillslopes 145
Introduction 145
Slope-Forming Materials 146
Strength of Rock and Soil 147
Effects of Weathering on Rock Strength 149
Diffusive Processes 150
Rainsplash 150
Sheetwash 151
Soil Creep 151
Mass Movements 153
Slides 154
Flows 156
Falls 158
Slope Stability 159
Driving and Resisting Stresses 159
Infinite-Slope Model 160
Environmental and Time-Dependent Effects 161
Slope Morphology 163
Weathering-Limited (Bedrock) Slopes 163
Transport-Limited (Soil-Mantled) Slopes 165
Threshold Slopes 166
Hillslope Evolution 166
Drainage Density 166
Box 5.1 Derivation of the Form of Convex Hillslope Profiles 167
Channel Initiation 170
Applications 172
Selected References and Further Reading 173
Digging Deeper: How Much Do Roots Contribute to Slope Stability? 174
Worked Problem 177
Knowledge Assessment 178
Channels 179
Introduction 179
External Controls on Fluvial Processes and Form 180
Discharge 181
Sediment Supply 181
Bed and Bank Material 181
Vegetation 184
Fluvial Processes 185
Flow Velocity 185
Discharge Variability 187
Stream Power 189
Box 6.1 Derivation of Stream Power 189
Bedrock Incision 189
Channel Migration 191
Sediment Transport 194
Initiation of Transport 194
Sediment Loads 197
Bedforms 198
Channel Patterns 199
Straight and Sinuous Channels 200
Meandering Channels 201
Braided Channels 201
Anastomosing Channels 201
Channel-Reach Morphology 202
Colluvial Reaches 202
Bedrock Reaches 202
Alluvial Reaches 202
Large Organic Debris 204
Floodplains 205
Channel Response 207
Applications 208
Selected References and Further Reading 209
Digging Deeper: What Controls Rates of Bedrock River Incision? 211
Worked Problem 214
Knowledge Assessment 214
Drainage Basins 217
Introduction 217
Basin-Scale Processes 219
Sediment Budgets 219
Sediment Routing and Storage 222
Channel Networks and Basin Morphology 223
Drainage Patterns 223
Channel Ordering 225
Downstream Trends 225
Uplands to Lowlands 227
Process Domains and Valley Segments 228
Longitudinal Profiles 230
Channel Confi nement and Floodplain Connectivity 231
Box 7.1 River Longitudinal Profi les 232
Downstream Trends 232
Drainage Basin Landforms 233
Knickpoints 233
Gorges 234
Terraces 235
Fans 237
Lakes 239
Applications 240
Selected References and Further Reading 244
Digging Deeper: When Erosion Happens, Where Does the Sediment Go? 245
Worked Problem 250
Knowledge Assessment 251
Coastal and Submarine Geomorphology 253
Introduction 253
Coastal Settings and Drivers 254
Tectonic Setting 254
Sea-Level Change 254
Salinity 256
Substrate and Sediment Supply 256
Tides 257
Waves 259
Coastal Processes and Landforms 264
Rocky Coasts 264
Beaches and Bars 266
Spits, Tidal Deltas, and Barrier Islands 268
Lagoons, Tidal Flats, and Marshes 270
Estuaries 271
Deltas 272
Coastal Rivers 274
Marine Settings and Drivers 274
Currents 275
Marine Sedimentation 276
Dissolved Load 276
Marine Landforms and Processes 276
Continental Margins 277
Abyssal Basins 278
Mid-Ocean Ridges 278
Trenches 279
Coral Reefs 279
Applications 281
Selected References and Further Reading 281
Digging Deeper: What Is Happening to the World’s Deltas? 283
Worked Problem 286
Knowledge Assessment 287
PART III
Ice, Wind, and Fire 289
Glacial and Periglacial
Geomorphology 291
Introduction 291
Glaciers 294
Glacier Mass Balance 294
Glacier Energy Balance 296
Accumulation and Ablation of Glacial Ice 297
Glacier Movement 299
Thermal Character of Glaciers 302
Glacial Hydrology 303
Subglacial Processes and Glacial Erosion 305
Glacial Sediment Transport and Deposition 309
Subglacial Sediments and Landforms 309
Ice-Marginal Sediments and Landforms 310
Glacially Related Sediments and Landforms 311
Glacial Landscapes, Landforms, and Deposits 313
Landforms of Alpine Glaciers 313
Landforms of Ice Sheets 314
Geomorphic Eff ects of Glaciation and Paraglacial Processes 315
Periglacial Environments and Landforms 316
Permafrost 317
Characteristic Periglacial Landforms and Processes 318
Applications 322
Selected References and Further Reading 323
Digging Deeper: How Much and Where Do Glaciers Erode? 324
Worked Problem 327
Knowledge Assessment 328
Wind as a Geomorphic Agent 329
Introduction 329
Air as a Fluid 331
Wind Patterns and Speeds 332
Vertical Distribution of Wind Speed 333
Settling Speed of Particles in Air 333
Spatial Distribution of Wind-Driven Geomorphic Processes 334
Aeolian Processes 335
Disturbance 335
Erosion 335
Sediment Transport 337
Deposition 341
Aeolian Features, Landforms, and Deposits 342
Aeolian Erosional Features and Landforms 342
Aeolian Transport Features and Landforms 343
Aeolian Dust Deposits and Loess 347
Applications 350
Selected References and Further Reading 351
Digging Deeper: Desert Pavements—The Wind Connection 352
Worked Problem 354
Knowledge Assessment 354
Volcanic Geomorphology 355
Introduction 355
Distribution and Styles of Volcanism 356
Magma Chemistry and Volcano Morphology 359
Tectonic Forcing and Volcanic Provinces 361
Eruptive Mechanisms and Products 363
Lava Flows 363
Pyroclastic Flows and Falls 365
Volcanic Gases 366
Eruption Sizes and Types 368
Volcanic Landscapes 368
Landscapes of Basaltic Volcanism 368
Landscapes of Silicic Volcanism 371
Processes of Volcanic Landform Evolution 372
Geomorphic Eff ects of Magma Intrusion 372
Biologic Colonization 373
Denudation and Aging 374
Mass Movements 374
Lahars 375
Volcano-River Interaction 377
Hydrologic Considerations 377
Erosional Landforms 380
Applications 381
Selected References and Further Reading 382
Digging Deeper: Geomorphic Eff ects of Volcano Sector Collapse 383
Worked Problem 386
Knowledge Assessment 387
PART IV
The Bigger Picture 389
Tectonic Geomorphology 391
Introduction 391
Tectonic Processes 392
Uplift and Isostasy 393
Thermal and Density Contrasts 397
Tectonic Settings 397
Extensional Margins and Landforms 399
Compressional Margins and Landforms 401
Transform Margins and Landforms 404
Continental Interiors 404
Structural Landforms 408
Landscape Response to Tectonics 411
Coastal Uplift and Subsidence 412
Rivers and Streams 413
Hillslopes 413
Box 12.1 Drainage Area-Slope Analysis 414
Erosional Feedbacks 415
Applications 417
Selected References and Further Reading 417
Digging Deeper: When and Where Did that Fault Last Move? 419
Worked Problem 422
Knowledge Assessment 423
Geomorphology
and Climate 425
Introduction 425
Records of a Changing Climate 427
Landform Records of Climate Change 427
Lake and Marine Sediment 429
Ice Cores 432
Windblown Terrestrial Sediment 433
Climate Cycles 434
Glacial Cycles 434
Orbital Forcing 436
Local Events—Global Effects 436
Climate Variability Within a Climate State 438
Short-Term Climate Changes 439
Geomorphic Boundary Conditions 439
Precipitation and Temperature 440
Vegetation, Fire, and Geomorphic Response 440
Base Level 442
Climatic Geomorphology 444
Köppen Climate Classifi cation 445
Climate-Related Landforms and Processes 445
Relict Landforms 446
Landscape Response to Climate 447
Glacial-Interglacial Changes 447
Isostatic Responses 448
Climatic Control of Mountain Topography 449
Climate Change Eff ects 449
Landscape Controls on Climate 452
Regional Climate 452
Earth’s Energy Balance 452
Hydrologic Cycling 452
The Atmosphere 454
Applications 454
Selected References and Further Reading 455
Digging Deeper: Do Climate-Driven Giant Floods Do Significant Geomorphic Work? 457
Worked Problem 459
Knowledge Assessment 460
Landscape Evolution 461
Introduction 461
Factors of Landscape Evolution 462
Tectonics 462
Climate 463
Topography 464
Geology 465
Biology 465
Models of Landscape Evolution 467
Conceptual Models 467
Physical Models 469
Mathematical Models 469
Landscape Types 471
Steady-State Landscapes 471
Transient Landscapes 474
Relict and Ancient Landscapes 478
Basin Hypsometry and Landscape Form 479
Rates of Landscape Processes 480
Uplift Rates 481
Erosion Rates 481
Spatial and Temporal Variability 483
Applications 487
Selected References and Further Reading 487
Digging Deeper: Is This Landscape in Steady State? 490
Worked Problem 493
Knowledge Assessment 494
Table of Variables T-1
Index I-1